2009 Yamaha RD350 Concept

Could this be the return of the two-stroke sportbike?

Two-stroke motorcycle engines are akin to the dodo bird – or nearly so. Ring-ding streetbikes all but disappeared by the 1990s, reaching their zenith in the mid-’80s with the GP-inspired Yamaha RZ500, Suzuki RG500 Gamma and Honda NSR400, all of which were never officially available in America but were sold nearly everywhere else. The sporting two-stroke bike movement petered out with the Yamaha RZ350 in the late ’80s, choked down with catalytic converters in its exhaust expansion chambers.

Indeed, it’s the two-stroke motor’s inherent oil-burning design that has forced it from roads in which exhaust emissions are now strictly controlled. Bimota’s innovative 500cc Vdue seemed to offer the promise of a clean-burning, lightweight two-stroke sportbike, but drivability issues with its fuel-injected V-Twin could never be fully resolved, and this failure (Bimota’s first and only attempt at building its own engine) eventually precipitated the Italian company’s demise until its resurrection a few years ago.

But now word comes out of Italy that the two-stroke streetbike might be experiencing its own resurrection, as these concept sketches of a Yamaha RD350 illustrate. As before, the challenge is to create a two-cycle engine that is able to pass emissions regulations, but perhaps the recent innovations in two-stroke outboard boat motor technology can be somehow adapted to a street-legal motorcycle engine. The challenge Bimota and others faced in this regard has been getting the air/fuel mixture in and out efficiently at the higher revs required of a bike engine. It’s possible that new fuel-injection technology and effective catalyzers might be able to solve this longstanding conundrum.

At this point, it seems doubtful that we’ll be riding new two-stroke sportbikes anytime soon, but these sketches certainly whet the appetites of those who regard these simple and lightweight motors as the ultimate in sportbike powerplants. A prediction of 65-75 rear-wheel horsepower seems doable, and we’d expect an aluminum-framed bike like this to weigh somewhere in the 320-lb range, giving it a power-to-weight ratio close to that of a contemporary 600cc sportbike.